Exercise bike



FIG. 1 is a perspective view of an exercise bike;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a left view thereof;

FIG. 5 is a right view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines illustrate environmental structure which form no part of the claimed design. 

The ornamental design for exercise bike, as shown and described. 